Scheduling apparatus and method for packet data service in a wireless communication system

ABSTRACT

Disclosed is a method for assigning packet data to be transmitted to a radio packet data channel of a base station system in response to a packet traffic transmission request for a plurality of mobile stations in a mobile communication system. The method comprises collecting the packet traffic transmission requests of the radio packet data channel for the mobile stations; selecting at least one of the mobile stations from the collected packet traffic transmission requests; transmitting to the selected mobile station a channel assignment message including information about a data rate, data transmission durations of the radio packet data channel and start points of the data transmission durations for the selected mobile station; and transmitting the packet data to the selected mobile station at the start time of the data transmission durations at the data rate.

PRIORITY

[0001] This application claims priority to an application entitled“Scheduling Apparatus and Method for Packet Data Service in a WirelessCommunication System” filed in the Korean Industrial Property Office onFeb. 1, 2000 and assigned Ser. No. 2000-4993, the contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to a traffic channelassignment apparatus and method for a wireless communication system, andin particular, to an apparatus and method for assigning a packet trafficchannel.

[0004] 2. Description of the Related Art

[0005]FIG. 1 shows the structure of a conventional wirelesscommunication network, and FIG. 2 shows a method for assigning a radiotraffic channel in the conventional wireless communication network ofFIG. 1.

[0006] Referring to FIGS. 1 and 2, a description will be made of amethod for assigning a radio channel to a mobile station in theconventional wireless communication network.

[0007] To assign a radio packet data channel to a mobile terminal, basestation controllers (BSCs) 111-11M inquire of associated basetransceiver systems (BTSs) 101-10N about whether it is possible toassign a radio packet data channel to the mobile station. Upon receiptof the radio packet data channel assignment request in step 211, the BTSdetermines in step 213 whether there is an available radio packet datachannel (for example, a supplemental channel (SCH) in a CDMA-2000system). In this case, the BTS also determines whether there isavailable power or whether there is an available code in the CDMAsystem. If it is possible to assign the radio packet data channel, theBTS transmits a channel assignment message to the BSC, reversesresources for the radio packet data channel to be assigned to the mobileterminal so that other mobile terminals cannot use it, and then,exchanges radio packet data channel assignment-related signal messageswith the mobile station, by performing steps 215-219. Otherwise, whenthere is no available radio packet data channel, the BTS transmits areject message to the BSC in step 221, and the BSC then attempts torequest assignment of the radio packet data channel after a lapse ofpredetermined time.

[0008] However, this radio traffic channel assignment method has thefollowing disadvantages. In the following description, a “radio trafficchannel” or a “radio packet traffic channel” is assumed to be identicalto a supplemental channel (SCH) for transmitting radio packet data.

[0009] First, describing channel assignment for the case where there isan available radio packet data channel, an assigned radio packet datachannel cannot be used by other users beginning at a predetermined timebefore the base station system (BSS) exchanges data with the mobilestation. That is, the radio packet data channel is previously assignedto the corresponding user beginning at the time when the BTS assigns thechannel, so that the assigned channel (or traffic channel) is wasteduntil before the traffics (or data) are actually exchanged. Thisconsiderably degrades performance of the radio packet data channel (ortraffic channel). For example, if it is assumed that it takes 300 ms toassign the radio packet data channel and the traffics are actuallychanged for about 300 ms between the mobile station and the base stationsystem, the total time for which the radio packet data channel isassigned to the corresponding mobile station will become 600 ms.However, since the time for which the traffics are actually exchanged is300 ms, the remaining 300 ms cannot be used by the other mobilestations, thus causing a waste of the assigned channel. As a result, theutilization efficiency of the radio traffic channel is decreased.

[0010] Second, since the radio packet data channel is assigned to aspecific user on a circuit basis, unless the user releases the channel,other users cannot use the corresponding resources, even though the userdoes not transmit and receive packet data over the radio packet datachannel. Therefore, there arises the low-channel efficiency problem andthe unfairness problem among the users. In addition, the user must paythe call fee for the total time for which the radio packet data channelwas assigned to him, even though he did not transmit and receive packetdata over the radio packet data channel. Hence, the user pays muchhigher call fees as compared with an amount of the packet data which wasactually exchanged over the radio packet data channel.

SUMMARY OF THE INVENTION

[0011] It is, therefore, an object of the present invention to provide ascheduling apparatus and method for reserving assignment of a radiopacket traffic channel for servicing packet data in a wirelesscommunication system.

[0012] It is another object of the present invention to provide anapparatus and method for assigning a radio packet traffic channel in awireless communication system.

[0013] It is further another object of the present invention to providean apparatus and method for assigning channels to a plurality of usersby introducing a packet switching technique, and immediately releasingthe assigned channels after the users complete the use of the assignedchannels.

[0014] It is yet another object of the present invention to provide aleg selection apparatus and method for assigning a packet data channelwhen there exists a plurality of legs in a base station system for awireless communication system.

[0015] It is still another object of the present invention to provide anapparatus and method for acquiring radio information for scheduling bycollecting radio information for assignment of a packet data channel ina base station system for a wireless communication system.

[0016] It is still another object of the present invention to provide anapparatus and method for solving a frame offset collision problem of apacket data channel in a base station system for a wirelesscommunication system.

[0017] It is still another object of the present invention to provide anapparatus and method for solving a mis-recognition problem of a packetdata channel assigned to a mobile station in a base station system for awireless communication system.

[0018] To achieve the above and other objects, there is provided amethod for assigning packet data to be transmitted to a radio packetdata channel of a base station system in response to a packet traffictransmission request for a plurality of mobile stations in a mobilecommunication system. The method comprises collecting the packet traffictransmission requests of the radio packet data channel for the mobilestations; selecting at least one of the mobile stations from thecollected the packet traffic transmission requests; transmitting to theselected mobile station a channel assignment message includinginformation about a data rate, data transmission duration of the radiopacket data channel and starting points of the data transmissionduration for the selected mobile station; and transmitting the packetdata to the selected mobile station at the start points of the datatransmission duration at the data rate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above and other objects, features and advantages of thepresent invention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

[0020]FIG. 1 is a diagram illustrating a structure of a conventionalwireless communication network;

[0021]FIG. 2 is a flow chart illustrating a method for assigning a radiotraffic channel in the conventional wireless communication system;

[0022]FIG. 3 is a diagram illustrating a structure of a wirelesscommunication network according to an embodiment of the presentinvention;

[0023]FIG. 4 is a diagram illustrating a method for assigning a radiotraffic channel in a wireless communication network according to anembodiment of the present invention;

[0024]FIG. 5 is a flow chart illustrating a procedure for assigning aradio traffic channel in a wireless communication system according to anembodiment of the present invention;

[0025]FIG. 6 is a diagram illustrating an example where a radio trafficchannel in the worst condition is assigned in a wireless communicationsystem;

[0026]FIG. 7 is a diagram illustrating a procedure for exchanging asignaling message for assigning a radio traffic channel in a wirelesscommunication network according to an embodiment of the presentinvention;

[0027]FIG. 8 is a flow chart illustrating a procedure for selecting legsduring radio packet data communication in a wireless communicationnetwork according to an embodiment of the present invention; and

[0028]FIG. 9 is a block diagram illustrating the detailed structure ofthe BTS shown in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0029] A preferred embodiment of the present invention will be describedherein below with reference to the accompanying drawings. In thefollowing description, well-known functions or constructions are notdescribed in detail since they would obscure the invention inunnecessary detail.

[0030] In the following description, it will be assumed that in order toassign a packet data channel and a packet traffic channel, asupplemental channel (SCH) is used for a radio packet data channel, ascheduling interval R_(SCHEDULING) _(—) _(INTERVAL) is set to 260 ms, adata transmission duration R_(DURATION) is set to 80 ms, and 3 of 5candidate mobile stations are selected when scheduling a radio packetdata channel. However, it would be obvious to those skilled in the artthat various changes may be made without departing from the spirit andscope of the invention.

[0031] Prior to a detailed description of a preferred embodiment of thepresent invention, a method for scheduling and assigning a packet datachannel in a wireless communication system according to the presentinvention will be described in brief.

[0032] An embodiment of the present invention introduces a reservation(or scheduling) technique for assignment of a radio packet data channel.Therefore, even though a radio packet data channel is assigned to aspecific mobile station, other users can use the radio packet datachannel before the specific mobile station can actually transmit andreceive a traffic over the assigned radio packet data channel.Accordingly, the radio packet data channel is constantly operatedwithout a pause on a pipe lining basis by multiple users. In thismanner, the wireless communication system can maximize efficiency of theradio channels for servicing the packet data by assigning the packetdata channels by the scheduling technique.

[0033] Further, in the embodiment of the present invention, the wirelesscommunication system introduces a packet switching concept so that themobile stations are rapidly assigned radio packet data channels andthen, immediately release the assigned radio packet data channels afterusing the channels for the assigned time. Therefore, the wirelesscommunication system can prevent the radio packet data channels havingthe limited high-class resources from being monopolized by minor users.

[0034] In addition, the embodiment of the present invention proposes aleg selection method for assigning a radio packet data channel whenthere exists a plurality of legs in a base station system, to therebyprovide good channel assignment capability even during a handoff.Further, the embodiment of the present invention proposes a method forenabling the base station system to collect radio information forassignment of the radio packet data channel so as to collect informationfor scheduling the packet data channel. Moreover, the embodiment of thepresent invention proposes a method for enabling the base station systemto perform efficient power control on the radio packet data channel, inorder to enable efficient power control in the CDMA-2000 internationalstandard environment. Furthermore, the embodiment of the presentinvention provides a method for enabling the base station system tosolve a frame offset collision problem of the radio packet data channel,so as to solve the problems which may occur when a frame offset of theCDMA (Code Division Multiple Access) system operates with a schedulingalgorithm. In addition, the embodiment of the present invention preventsa malfunction problem of the mobile station by proposing a method forenabling the base station system to solve a mis-recognition problem of aradio packet data channel assignment message, which may occur in themobile station.

[0035] Now, a detailed description will be made of the foregoingembodiment of the present invention.

[0036] The method for assigning and scheduling a radio traffic channel,proposed in the invention, is based on the CDMA system, and can beapplied to every high-speed transmission environment. Therefore, theembodiment of the present invention can be applied to a CDMA-2000system, a UMTS system and a wideband CDMA system, which are all based onthe CDMA system and can provide a high-speed radio data transmissionservice.

[0037] Herein, the description of the present invention will be madewith reference to a wireless communication network based on theCDMA-2000 system.

[0038] The method for assigning and scheduling the radio trafficchannel, proposed in the embodiment of the present invention, isperformed in a wireless communication network shown in FIG. 3. Asillustrated in FIG. 3, the wireless communication network, to which thepresent invention is applicable, includes the following elements.

[0039] With respect to terminology, a mobile station (MS) iscommunication equipment carried by a mobile subscriber. The mobilestation is a CDMA-based device, which can support a voice service, adata service, and a combined service of voice and data. A base stationsystem (BSS) is equipment for performing direct communication with themobile station in the wireless communication network. The base stationsystem performs management of the radio resources, mobility control ofthe mobile station, and interfacing with a wired communication network.

[0040] In particular, the base station system is comprised of basetransceiver systems (BTSs) 101-10N and base station controllers (BSCs)111-11M. The BTSs 101-10N chiefly manage the radio resources throughdirect interfacing with the mobile station, and the BSCs 111-11M eachcontrol their associated BTSs 101-10N. Here, the BSC and the BTS canalso be united into one device. However, in most cases, they areseparated such that a plurality of BTSs are connected to one BSC. Theembodiment of the present invention is applied to the latter case, whichhas a tree structure or a star or ring structure in which a plurality ofBTSs 101-10N are connected to one BSC as shown in FIG. 3.

[0041] A mobile switching system (MSC) 120 supports a gateway functionfor a wired voice switching network such as a public switched telephonenetwork (PSTN) for the voice service, and supports interworking with apacket data network through an interworking function (IWF) device 150for the circuit data service. In the following description, the wiredvoice switching network will be assumed to be a PSTN. In addition, theMSC 120 supports mobility management of the mobile station throughinterfacing with a home location register (HLR) 121 and a visitorlocation register (VLR) 123.

[0042] The HLR 121 is a device for storing a home location of the mobilestation. The HLR 121 stores location-related information of thesubscribers and principal subscription information such as QoS (Qualityof Service) information.

[0043] The VLR 123 performs location management at the present mobilestation's area in order to trace the location of the mobile station whenthe present location of the mobile station is not the home location.

[0044] A packet data serving node (PDSN) 130 interlinks a wired packetdata service network 140 with the BSCs 111-11M. The data communicatedthrough the PDSN 130 is the packet data, and is linked to the wiredpacket data service network 140.

[0045] The embodiment of the present invention is applied to the mobilestation and the base station system shown as elements in the wirelesscommunication network of FIG. 3. In the following description, the term“base station system (BSS)” will be defined as a device comprised of thebase station controller (BSC) and the base transceiver system (BTS). Inaddition, it will be assumed herein that the wireless communicationnetwork is based on the CDMA-2000 system. Further, although the wirelesscommunication network has been described with reference to the existingmobile communication network including the MSC, HLR, VLR and PDSN, thepresent invention can also be applied to a different mobilecommunication network structure including other elements similar to theMSC, HLR, VLR and PDSN.

[0046] Next, an operation of the embodiment will be described withreference to a radio channel structure of the CDMA-2000 wirelesscommunication network.

[0047] In order to support the radio data service, the mobile stationand the base station system require a path over which they can exchangesignaling information, and this path is called a channel. In theCDMA-2000 system, the channels for exchanging the signaling informationinclude a fundamental channel (FCH) and a dedicated control channel(DCCH), and the mobile station and the base station system can exchangesignaling messages using these channels. Here, the FCH is used fortransmitting voice signals and the DCCH is used for transmitting controlinformation. Further, both the FCH and DCCH can perform a function ofexchanging dedicated control information with the mobile station insession. Although it is possible for the FCH and the DCCH to transmitand receive the traffics for the packet data service, these channelstransmit and receive a very small amount of the packet data through apath with a very low data rate. Further, a packet data service using theFCH and DCCH does not separately require channel assignment andscheduling. Therefore, an operation of transmitting and receiving thepacket data over the FCH and DCCH will be omitted in the followingdescription.

[0048] However, unlike in the FCH and the DCCH, exchange of high-speedpacket data between the mobile station and the base station system isperformed through a separate dedicated channel. For example, theCDMA-2000 system includes a supplemental channel (SCH) for exclusivelycommunicating the data, and supports a high-speed radio packet dataexchange function between the base station system and the mobile stationby using the SCH channel. The relationship between the SCH and theFCH/DCCH is as follows. The FCH and the DCCH are maintained even whenthere is no data exchange between the mobile station and the basestation system, and these channels are chiefly used for transmitting andreceiving the signaling messages. Therefore, when an amount of thepacket data traffic to be exchanged is increased, the base stationsystem assigns an SCH channel for communicating the packet data at thehigh data rate by exchanging the signaling messages over the FCH or theDCCH with the mobile station. When the SCH is assigned, the high-speedpacket traffics are exchanged between the mobile station and the basestation system over the SCH. Thereafter, when there is no traffic totransmit and receive, the base station system and the mobile stationexchange signaling messages for releasing the assigned channel over theFCH and the DCCH, and then, release the assigned SCH. Here, it is alsopossible to release the assigned SCH channel without exchanging thesignaling messages for releasing the assigned channel between the basestation system and the mobile station.

[0049] Therefore, the high-speed radio traffic channel used in themethod for scheduling, assigning and releasing the packet trafficchannel, according to an embodiment of the present invention, is assumedto be mapped to the SCH channel of the CDMA-2000 system, and the path(or channel) for exchanging the signaling messages for assigning thehigh-speed radio traffic channel between the mobile station and the basestation system is defined as the FCH or DCCH.

[0050] Now, a detailed description of the embodiment of the presentinvention will be made.

[0051] In the high-speed wireless communication network, a CDMA-2000base station system according to an embodiment of the present inventionschedules a radio traffic channel on a packet switching basis and then,assigns the packet traffic channel according to the scheduling results.

[0052] In general, the radio traffic channel can be assigned in twodifferent methods: one is a circuit method and another is a packetswitching method. The circuit method has a structure in which a radiotraffic channel is assigned to a specific mobile station and then, otherusers cannot use the assigned radio traffic channel regardless ofwhether the specific mobile station actually transmits and receives thetraffic over the assigned channel, as in the traffic channel assignmentin voice service. The packet switching method has a structure in whichonly the subscriber who actually needs to transmit and receive thepacket requests assignment of the radio traffic channel, and anassignment time of the radio traffic channel is also limited. Therefore,when the channel is assigned in the packet switching method, a “pipe” isassigned to every user for a predetermined time and after the expiry ofthe time, the pipe is assigned to another user. In the followingdescription, the term “pipe” will have the same meaning as the term“channel”. In general, the circuit method is applied to, for example, avoice service in which the traffic arrives continuously. However, thepacket switching method is applied to, for example, an Internet servicein which the traffic has a burst property and thus arrivesintermittently. The circuit method can be supported in the same methodas used in assigning the voice channel.

[0053] Therefore, in the embodiment of the present invention, processingthe SCH on the circuit basis is assumed be performed as follows. Herein,a technique for assigning and scheduling a radio traffic channel on thepacket switching basis will be described, while a description of amethod for operating a radio packet data channel on the circuit basiswill not be provided. In addition, it will be assumed herein that thescheduling method described in the embodiment of the present inventionis performed on the band remaining after supporting the voice call andthe circuit data call.

[0054] In the embodiment of the present invention, several new terms aredefined as follows, in order to assign and schedule the radio trafficchannel.

[0055] First, the term “radio traffic channel assignment time” isdefined as an SCH setup time (SS_Time), since the radio traffic channelis the SCH in the CDMA-2000 system. The radio traffic channel assignmenttime is a time required when the base station system and the mobilestation complete preparations for transmitting and receiving the radiotraffic channel and then actually transmit and receive the traffic bystarting radio traffic channel processing, after a scheduler for theradio traffic channel determines assignment of the radio traffic channel(SCH). As the radio traffic channel assignment time becomes shorter, itis possible to rapidly assign the radio traffic channel.

[0056] The radio traffic channel assignment time can be set to 0 ms,when there is no need to continuously exchange the signaling messagesfor assigning the radio traffic channel between the base station systemand the mobile station, as in the method using the variable data rate,the discontinuous transmission of the SCH and the scrambling code.

[0057] Second, the term “scheduling interval of the radio trafficchannel” refers to a scheduler operation parameter R_(SCHEDULING) _(—)_(INTERVAL) described below. The scheduling interval of a radio trafficchannel indicates an interval for which the radio traffic channelscheduler is periodically activated to operate. As the assignment andscheduling interval of the radio traffic channel becomes shorter, thesystem load increases more and more, but it is possible to efficientlytransmit the packet data traffic and to rapidly cope with the change inthe radio channel.

[0058] Third, the term “transmission unit time of the radio trafficchannel” is a minimum time unit required in assigning the radio trafficchannel, and N times the minimum time unit (where N=1, 2, 3, 4, . . . )is defined as a data transmission duration R_(DURATION). In thefollowing description, it will be assumed that the transmission unittime of the radio traffic channel is 20 ms, since a frame period of thedata transmitted over the SCH channel is 20 ms in the CDMA-2000 system.In the embodiment of the present invention, R_(DURATION) will bereferred to as “data transmission duration” for transmitting the packetdata over the radio packet data channel. As the unit time fortransmitting the data over the radio traffic channel becomes shorter,the radio traffic channel is more frequently assigned and released,causing an increase in an amount of the channel assignment-relatedmessages being exchanged between the mobile station and the base stationsystem in the wireless link.

[0059] The embodiment of the present invention manages assignment andscheduling of a forward radio traffic channel transmitted from the basestation system to the mobile station. In this connection, the radio dataservice generally has an asymmetric property. That is, there is a smallamount of the packet traffic on the reverse link transmitted from themobile station to the base station system, whereas there is a greatamount of the packet traffic on the forward link transmitted from thebase station system to the mobile station. Therefore, in order tomaximize the efficiency of the radio resources, it is necessary toincrease the efficiency of the forward radio traffic channel. Therefore,in the embodiment of the present invention, it will be assumed that onlyan operation of the forward radio traffic channel is considered, and achannel having a low data rate is assigned for the reverse radio trafficchannel. In addition, it will be assumed that assignment of the reverseradio traffic channel (R-SCH) follows a call admission control (CAC)process of the FCH and the DCCH.

[0060] In the embodiment of the present invention, it is possible toprovide a simple structure and a complex structure by controlling anoperation parameter. For example, to support the simple structure, themethod according to an embodiment of the present invention can set theoperation parameter as follows. That is, a single radio traffic channelstructure is supported as a fat-pipe structure (i.e., a structure foroperating one or a small number of the SCH channels in order to transmitthe packet data at a high data rate), and the duration R_(DURATION) fortransmitting data over the radio traffic channel is equally assigned tothe subscribers, thereby facilitating the development and experiment ofsystem parameters.

[0061] It might be necessary to adjust several parameters whenimplementing the embodiment of the present invention. That is, when theembodiment of the present invention is applied to the CDMA-2000 system,there may arise the following limitations, which are adaptive to thetechnologies to be applied and exert no influence on the substance ofthe invention.

[0062] First, when it is intended to maximize a quality of the voiceservice, the power allocated for the data service according to a voiceband allocation value α can be used for the channel assignment for thedata service during the CAC process, and the power remaining in thevoice service band during SCH scheduling cannot be used for SCHassignment. That is, in the embodiment of the present invention, it isassumed that the remaining power, except the power set for the voiceservice, is used for the SCH assignment. However, in order to increase aprocessing rate of the data service, it is also possible to use theunused power in the voice service band (i.e., the reserve powerpresently unused for the voice service out of the power set for thevoice service).

[0063] Second, the base station system (BSS) performs scheduling toassign the SCH to the mobile stations in a unit of the set schedulinginterval R_(SCHEDULING) _(—) _(INTERVAL). In the embodiment of thepresent invention, the scheduling interval R_(SCHEDULING) _(—)_(INTERVAL) is assumed to be 260 ms. However, it is also possible to setthe scheduling interval of the SCH to over or below 260 ms.

[0064] Third, the base station system (BSS) collects radio informationfor the SCH scheduling at intervals of 260 ms.

[0065] Fourth, when a frame offset of the SCH is the same as that of theFCH/DCCH, there may occur a frame offset collision between thesubscribers assigned the SCH in the same scheduling interval. To preventthis, the frame offset of the SCH is assigned separately from theFCH/DCCH, or a guard interval is assigned to disperse the collisionpoints when there exists no frame offset of the SCH.

[0066] Fifth, when the base station system (BSS) is divided into thebase station controller (BSC) and the base transceiver system (BTS), theBSC can support the flow control with the BTS such that a predeterminedamount of RLP (Radio Link Protocol) packets exist in the BTS.

[0067] Sixth, the BTS supports RLP packet buffering, sequencemanagement, and reservation of RLP packet transmission during DTX(Discontinuous Transmission), and reports “a sequence of the lasttransmitted RLP packet” to the BSC through an inband path.

[0068] Seventh, in the embodiment of the present invention, the datatransmission duration R_(DURATION) of the SCH is assumed to be 80 ms.However, it is also possible to set the data transmission duration ofthe SCH to over or below 80 ms.

[0069] Eighth, ESCAM (Extended Supplemental Channel Assignment Message)for the SCH assignment can avoid an ACK/NACK process.

[0070] Ninth, when the FCH/DCCH supports a soft handoff so that thereare two or more legs for the mobile station, a leg selection algorithmis performed. One of the two or more legs is selected by performing theleg selection algorithm. Here, the leg is one of the base transceiversystems (BTSs).

[0071] In addition, the following operation parameters are defined inthe invention.

[0072] The “scheduling interval R_(SCHEDULING-INTERVAL)” indicates atime for which a radio traffic channel scheduler is periodicallyactivated to assign and schedule the radio traffic channel.

[0073] Preferably, a value of the scheduling intervalR_(SCHEDULING-INTERVAL) should be set to be larger than or equal to atime value required when the base station system (BSS) assigns the radiotraffic channel to the mobile station (R_(SCHEDULING-INTERVAL)≧(a timerequired when the base station system assigns the radio traffic channelto the mobile station)).

[0074] The “data transmission duration R_(DURATION)” is a duration forwhich the radio traffic channel scheduler assigns the radio trafficchannel to the mobile stations, and the data transmission duration ofthe radio traffic channel indicates a duration (or time) for which thecorresponding mobile station can exclusively communicate with the basestation system through the radio packet data channel for the durationD_(DURATION). In the embodiment of the present invention, the datatransmission duration is assumed to be 80 ms, as stated above. Further,in the embodiment of the present invention, the duration R_(DURATION) isequally set for every mobile station. However, it is also possible tovariably set the duration R_(DURATION) depending on the classificationof the mobile stations.

[0075] “β” is a time value required in sorting the frame offset, whenthere exists a frame offset of the radio traffic channel in theCDMA-2000 system, and the value β is defined as 20 ms. When the frameoffset of the radio traffic channel is 0 ms, the value β is set to 0.

[0076] Table 1 below shows recommended parameter values for the methodof scheduling the SCH of the CDMA-2000 system according to an embodimentof the present invention. TABLE 1 R_(SCHEDULING_INTERVAL) R_(DURATION)1^(st) Recommended Value 260 ms 80 ms (Default) (= 80 ms × 3 + β ms)2^(nd) Recommended Value 260 ms 40 ms (Optional) (= 40 ms × 6 + β ms)

[0077] For the description of the packet channel assignment andscheduling technique, the embodiment of the present invention will beconsidered with reference to the base station system (BSS) which isdivided into the BSC and the BTS. In addition, the embodiment will bedescribed with reference to an environment in which the BSC and the BTSare logically implemented in several processors. This is to give a cleardescription of the present invention. In practice, however, the severalprocessors can be designed into one processor, and the BSC and the BTScan also be designed into a single base station system device. Inparticular, the embodiment of the present invention will be describedwith reference to only the processors required when supporting the radiopacket data service.

[0078] First, a description will be made of the BSCs 111-11M shown inFIG. 3.

[0079] A main media control processor (MMCP) is a media controlprocessor, which supports a function of controlling a path fortransmitting and receiving the actual packet data and supports an errorcontrol function. In the CDMA-2000 system, the MMCP provides interfacingwith an RLP (Radio Link Protocol) layer, a MAC (Medium Access Control)layer, and a wired Internet network. The MMCP provides an RMCP (RadioMedia Control Processor) with the packet data to be transmitted to therespective users, by using the flow control function.

[0080] A main call control processor (MCCP) is a call control processor,which provides a principal function of processing the signaling messagesbetween the mobile station and the base station system, and a functionof transmitting and receiving a radio traffic channel assignmentmessage. In addition, the MCCP supports a function of collectinginformation about pilot strength received from the mobile station andproviding the collected pilot strength information to the MMCP.

[0081] Second, a description will be made of the structure of the BTSs101-10N shown in FIG. 3.

[0082] A radio resource management processor (RRMP) supports a functionof assigning the radio traffic channel to specific users by consideringthe radio channel information together with radio media controlprocessor (RMCP) buffer information of the BSC. The RRMP is a processorfor performing the scheduling function to actually assign the radiotraffic channel. That is, the RRMP has an SCH scheduling functionaccording to an embodiment of the present invention.

[0083] A radio information measurement processor (RIMP) performs afunction of collecting the radio channel information and providing thecollected radio channel information to the BSC and the RRMP.

[0084] A radio media control processor (RMCP) buffers the packet data ofthe respective users received from the MMCP through the flow controlfunction, and requests assignment of the SCH radio traffic channel byproviding the RRMP with information about amount of the buffered userpacket. When the radio traffic channel is assigned by the RRMP, the RMCPtransmits the received packets to the radio traffic channel for theassigned time.

[0085] In the embodiment of the present invention, an operation ofscheduling and assigning the radio packet traffic channel will bedescribed with reference to the CDMA-2000 communication system.

[0086]FIG. 4 shows a method for assigning and scheduling a packettraffic channel in the wireless communication network of FIG. 3according to an embodiment of the present invention.

[0087]FIG. 4 shows a scheduling operation for the case where thehigh-speed radio packet traffic channel is an SCH in the CDMA-2000system. With reference to FIG. 4, an operation according to theembodiment of the present invention will be described step by step.Here, the RRMP includes a function of a collector for collecting an SCHuse request signal to schedule and assign the radio traffic channel, afunction of a scheduler for scheduling use of the SCH, and a function ofa message generator for generating a scheduling message using thescheduled results.

[0088] In FIG. 4, intervals t₀-t₁, t₁-t₂, t₂-t₃, t₃-t₄, t₄-t₅, . . . arescheduling intervals R_(SCHEDULING) _(—) _(INTERVAL) and in theembodiment of the present invention, each interval is 260 ms. At step410, in the interval t₀-t₁, the collector of the RRMP collects the SCHuse request. In the interval t₁-t₂, the scheduler is activated to assignthe channel (step 420) by scheduling the mobile stations so that theycan use the SCH in an interval following the point t₂, and the messagegenerator generates a channel assignment message (here, an ESCAMmessage) for the mobile stations. Here, the SCH use request signalcollected by the collector is generated in the RMCP of the base stationsystem. That is, the SCH scheduling according to an embodiment of thepresent invention is applied to the SCH of the forward link.Accordingly, the SCH use request signal is generated when it isnecessary to transmit packet data on the forward link. Therefore, theSCH use request signal is generated by the base station system when thebase station system transmits packet data to a specific mobile stationover the SCH of the forward link. In addition, when the channelassignment messages are simultaneously transmitted to the channelassignable mobile stations, the packet data has a burst property becauseof the messages. Accordingly, it is preferred to distribute the channelassignment messages as shown in step 430 of FIG. 4. Here, the channelassignment message includes information about a start time of the SCH, adata rate of the SCH channel and a data transmission durationR_(DURATION). Then, in the interval t₂-t₃, at step 440, the mobilestations communicate the radio packet data over the SCH at the set starttime at the set data rate for the set data transmission durationR_(DURATION). In the interval t₂-t₃ of the SCH channel, the base stationsystem (BSS) transmits the packet data for the corresponding mobilestations in the data transmission duration R_(DURATION) of the radiotraffic channel shown by reference numeral 450. That is, the basestation system can sequentially transmit the packet data to a pluralityof the mobile stations (3 mobile stations in FIG. 4) in one schedulinginterval according to the scheduled order. The mobile stations then turnON the SCH at the start point of the assigned data transmission durationto receive the packet data, and automatically turn OFF the SCH at an endpoint of the data transmission duration.

[0089] To sum up, in the first scheduling interval t₀-t₁, the SCH userequest signal is collected (step 410) as shown in FIG. 4. In the secondscheduling interval t₁-t₂, the scheduler of the base station system isactivated (step 420) to assign the SCH by scheduling the mobile stationsaccording to the collected SCH use request. The SCH is assigned suchthat the mobile stations have different start points of the SCH in onescheduling duration (step 430). Then, the channel assignment messagesincluding information about the data rate to be used at the set startpoint and the transmission duration are generated, and the generatedchannel assignment messages are transmitted at distributed startingpoints to the corresponding mobile stations. Thereafter, in the thirdscheduling interval t₂-t₃, the base station system sequentiallytransmits the radio packet data to the mobile stations over the SCH atthe set start points according to the channel assignment messages (step440).

[0090] The above SCH scheduling and assignment operation is continuouslyperformed. That is, when the SCH is used as shown in FIG. 4, thecollector collects the SCH the packet traffic transmission requestsincluding a, c and d mobile stations in the interval t₀-t₁.

[0091] In the interval t₁-t₂, the scheduler is activated to schedule thea, c and d mobile stations intended to use the SCH channel, and themessage generator generates the SCH assignment message according to thescheduled results and transmits the generated message. At this moment,the collector collects the SCH the packet traffic transmission requestsincluding b, g and w mobile stations.

[0092] In the interval t₂-t₃, the RMCP transmits the radio packet datato the SCH-assigned mobile stations a, c and d over the SCH for the setdata transmission duration R_(DURATION). In addition, the scheduler isactivated to schedule the b, g and w mobile stations, and the messagegenerator generates the SCH assignment message according to thescheduled results and transmits the generated message, At this moment,the collector collects the SCH the packet traffic transmission requestsincluding a, c and h mobile stations.

[0093] As described above, it is noted that the SCH use request, theassignment of the SCH channel, and transmission of the radio packet datathrough the assigned SCH are simultaneously performed in each schedulinginterval. Such an operation is continuously performed. In addition, itis noted from the foregoing description that the assignment and releaseof the SCH is performed at the scheduling intervals. Therefore, the SCHchannel is rapidly assigned and released, thus making it possible tomaximize utilization efficiency of the SCH.

[0094] The detailed description of the above operation will be madebelow.

[0095] First, in step 410 of FIG. 4, when the base station system haspacket data to transmit to the mobile stations, the RMCP generates anSCH use request signal and the collector in the RRMP collects the SCHuse request information.

[0096] More specifically describing an operation of the step 410, thetraffics received from the wired packet data network are buffered by theMMCP in the BSC, and the MMCP provides the BTS with information aboutarrival of the packet and amount of the received traffics. In this case,the information provided to the BTS may include only the buffer sizeinformation of the MMCP, or the actual RLP packet can be provided to theRMCP of the BTS through the flow control function between the RMCP andthe MMCP. The embodiment of the present invention will be described withreference to the case where the actual traffic is provided to the RMCP.The RMCP provides the data amount information of the RMCP buffer to theRRMP in the BTS. As a method for informing the RRMP of the buffer size,the RMCP periodically provides either the entire MS information in theRMCP or the buffer size information of the individual MS so that theRRMP collects the information.

[0097] Second, in step 420 of FIG. 4, the scheduler is activated toassign the SCH for the mobile stations intended to use the SCH in thenext scheduling interval.

[0098] More specifically describing an operation of the step 420, theSCH channel assignment algorithm of the RRMP is activated at everyscheduling interval R_(SCHEDULING) _(—) _(INTERVAL). For theintellectual application of QoS (Quality of Service) in the RRMP, it ispossible to apply a PFQ (Pseudo Fair Queuing) algorithm. The RRMPassigns information about an SCH code number, a start time, and a datatransmission duration R_(DURATION) of the radio traffic channel to thecorresponding MS according to the SCH channel assignment algorithm. TheRRMP provides the SCH assignment message to the MCCP according to theassigned information. The RRMP provides the SCH assignment message tothe RMCP to process the buffering and start time.

[0099] Third, in step 430 of FIG. 4, the SCH channel assignment messagesassigned in step 420 are dispersedly transmitted to the mobile stations,such that the messages are distributed at intervals of time.

[0100] More specifically describing an operation of the step 430, theMCCP exchanges signaling messages with the mobile stations according tothe received SCH assignment messages. The start points where the BSSstarts exchanging the signaling messages for the SCH assignment aredistributed over the scheduling interval R_(SCHEDULING) _(—) _(INTERVAL)according to the start time assigned to the respective mobile stations.

[0101] Fourth, in step 440 of FIG. 4, the respective mobile stationscommunicate the RLP packet data to the base station system over the SCHchannel at the set start time for the set transmission duration.

[0102] More specifically describing an operation of the step 440, theMMCP provides the RLP packet to the RMCP through the flow controlfunction according to the data rate and the data transmission durationof the radio traffic channel, and the RMCP transmits the traffic at theassigned start time at the set data rate for the data transmissionduration R_(DURATION) of the radio traffic channel.

[0103] Fifth, in step 450 of FIG. 4, the RLP packet data is actuallytransmitted over the SCH channel between the base station system and themobile stations in the scheduling duration.

[0104] More specifically describing an operation of the step 450, thestart time and the data rate for transmission of the radio packet,assigned in the RRMP, may be different for the respective subscribers.In step 450, the number of the SCH channels is assumed to be one.However, the number of the SCH channels can be greater than one. Thetransmission start time of the radio packet traffic transmitted over theSCH channel can be different for the respective subscribers in the nextscheduling interval R_(SCHEDULING) _(—) _(INTERVAL). In step 450, it isassumed that the packet traffic data transmission duration R_(DURATION)is fixed to a specific value of, for example, 80 ms. However, the datatransmission duration R_(DURATION) can be variably set according to thesubscribers.

[0105] That is, in the radio packet data channel communication devicefor the base station system in the mobile communication system accordingto an embodiment of the present invention, the RRMP performs a functionof the collector for collecting the SCH the packet traffic transmissionrequests, a function of the scheduler for scheduling use of the SCHchannel, and a function of the message generator for generating messagesaccording to the scheduled results. First, describing an operation ofthe collector, the RMCP receives the radio packet data channel thepacket traffic transmission requests transmitted from the mobilestations and transmits the received channel the packet traffictransmission requests to the RRMP, and then, the collector in the RRMPcollects the channel the packet traffic transmission requests from theRMCP. Second, describing an operation of the scheduler, the RRMP selectsat least one of the mobile stations which had requested use of the radiopacket data channel, so as to schedule the radio packet data channel,and then, the selected mobile station determines the data rate, the datatransmission duration in which the radio packet data channel can beused, and the start time of the data transmission duration. Third,describing an operation of the message generator, the RRMP transmits thedetermined SCH assignment information to the RMCP, the RMCP transmitsthe channel assignment message to the MMCP of the BSC through the inbandpath, and the MMCP transmits the received channel assignment message tothe MCCP. The MCCP then generates the radio packet data channelassignment messages including the SCH assignment information.

[0106] Then, a channel transmitter for the physical layer of the BTStransmits the radio packet data channel assignment message to the mobilestation. Thereafter, the channel transmitter transmits data over theradio packet data channel at the scheduled start point for thedetermined transmission duration, and releases the SCH channel to themobile station at a transmission end point.

[0107]FIG. 5 shows a traffic channel assignment algorithm according toan embodiment of the present invention. The RRMP performs the radiotraffic channel assignment and scheduling operation at the schedulinginterval R_(SCHEDULING) _(—) _(INTERVAL).

[0108] Referring to FIG. 5, in step 511, the RRMP of the BTSperiodically collects the SCH the packet traffic transmission requestsfrom the mobile stations and activates a program for assigning andscheduling the radio traffic channel. In the CDMA-2000 system, since theradio traffic channel is mapped to the SCH channel, a module forassigning and scheduling the radio traffic channel will be called an SCHscheduler. In step 513, the SCH scheduler selects the mobile stationswhich can use the SCH channel, out of the mobile stations which haverequested use of the SCH channel. In the embodiment of the presentinvention, it is assumed that the SCH scheduler first selects 5 mobilestations out of the mobile stations which have requested use of the SCHchannel, and then selects 3 mobile stations out of the selected 5 mobilestations. Therefore, in the embodiment of the present invention, it isassumed that 3 mobile stations can use the SCH in one schedulinginterval. For the method for selecting the 5 candidate mobile stationsin step 513, it is possible to apply an intellectual QoS supportingscheme such as the PFQ (Pseudo Fair Queuing) algorithm, and as a result,the candidate subscribers to which the SCH is to be assigned areselected. Here, the QoS parameters may include the subscriber class, themessage class and the data size. Thereafter, in step 515, the SCHscheduler finally selects the mobile stations which have no frame offsetcollision in the environment where the SCH uses the frame offset, basedon the 5 candidate mobile stations. The embodiment of the presentinvention will be described with reference to the case where the numberof the finally selected mobile stations is 3. Thereafter, in step 517,the scheduler calculates the data rate of the SCH channel, the starttime of the SCH channel and the end point of the SCH channel (i.e., anend point of the data transmission duration), for the respectiveselected subscribers.

[0109] In steps 519 and 521, the SCH scheduler updates a schedulerdatabase using the last calculated information and then, sends the MCCPa request for exchange of the SCH assignment message with the mobilestation. At this moment, the MCCP of the BSC dispersedly transmits theSCH assignment messages based on the SCH assignment start time for therespective mobile stations. By doing so, it is possible to suppress anincrease in the noises occurring when the SCH assignment messages aresimultaneously transmitted over the radio channel. In addition, bydispersedly transmitting the SCH assignment messages, it is possible tosolve a problem that the SCH assignment message assigned to the mobilestation in the previous scheduling interval is confused with the presentSCH assignment message. That is, in the CDMA-2000 mobile communicationsystem to which the present invention is applied, if the SCH assignmentmessage is received in the previous scheduling interval and a new SCHassignment message is received in the next scheduling interval beforetransmitting and receiving data over the assigned SCH, the mobilestation will confuse the two SCH assignment messages. In this case, themobile station discards the first received SCH assignment message.Therefore, if the SCH assignment messages are dispersedly transmitted asstated above, the mobile station receives the next SCH assignmentmessage at the point (or after the point) where the message istransmitted over the previously assigned SCH channel, thus solving theconfusion problem.

[0110] Thereafter, in steps 523 and 525, the base station system waitsuntil SCH assignment message transmission time arrives. Herein, when theSCH assignment message time arrives, the base station transmits the SCHassignment message in step 527. In addition, in step 529, if thereremains any SCH assignment message, which waits for the arrival of theSCH assignment message transmission time, then the procedure returns tostep 523. Meanwhile, in steps 527 to 529, when start time included inthe arrived SCH assignment message comes, data transmission is performedduring the transmission duration at a set data rate. According to thepreferred embodiment of the present invention, the above operation isrepeated three times.

[0111] It is possible that the scheme proposed in the invention mighthave limitations due to the frame offset of the SCH in the currentCDMA-2000 standard. A solution of this problem is shown in FIG. 6. Asshown by reference numeral 640, “[1]” indicates a point where thescheduler makes a decision, “[2]” indicates a point where the SCH isassigned to the mobile station, “[3]” indicates a point where the mobilestation is ready to process the SCH, and “[4]” indicates a point wherethe SCH opens at the start time.

[0112] Referring to FIG. 6, as shown by reference numeral 610, the SCHmessages are dispersedly exchanged at the start points of eachtransmission duration. As shown by reference numeral 620, the users areselected based on the frame offset and the previous scheduling intervalinformation. That is, when the frame offset of the SCH is assigned to beequal to the frame offset of the FCH/DCCH, the users assigned to thepresent scheduling interval R_(SCHUDULING) _(—) _(INTERVAL) are selectedfrom the users selected by the PFQ algorithm based on the followingcriteria. Five candidate subscribers assigned the SCH in the PFQalgorithm are first selected, and the scheduler then selects 3subscribers who have no frame offset collision, out of the subscribersselected as a result of the PFQ. In this case, when the subscriber whowas assigned the last RLP frame data transmission duration R_(DURATION)in the previous scheduling interval is selected as a candidate by thePFQ in the present scheduling interval R_(SCHEDULING) _(—) _(INTERVAL),the selected candidate subscriber is assigned to the last datatransmission duration R_(DURATION) of the present scheduling intervalR_(SCHEDULING) _(—) _(INTERVAL) in order to avoid the collision betweenthe data transmission durations R_(DURATION) of the radio trafficchannel due to the scheduling setup time (SS_Time). When there stilloccurs the frame offset collision, another subscriber is assigned to thelast data transmission duration.

[0113] That is, in the data transmission duration (i.e., G and H user'sdata transmission durations) before an A user transmits the packet dataover the assigned SCH in an interval T₁-T₂ of FIG. 6, it is scheduledthat the SCH assignment message to be used by the A user in the nextinterval T₂-T₃ is not transmitted. Herein, in case that the SCHassignment message of A user to be assigned in the interval T2-T3 istransmitted before the packet data of A user is transmitted in theinterval T1-T2, data of A user between in the interval T1-T2 and inT2-T3 may be interfered with each other. In addition, as shown byreference numeral 630, if only one mobile station (i.e., the A user inan interval T₃-T₄ of FIG. 6) intends to use the SCH, the RRMP schedulercan assign the entire data transmission duration R_(DURATION) (i.e., aninterval T₄-T₅ of FIG. 6) of the radio traffic channel in the schedulinginterval to the single mobile station, as in the third SCH assignmentprocess for the A user in FIG. 6.

[0114]FIG. 7 shows a call processing procedure for assigning andscheduling a radio packet traffic channel in the CDMA-2000 systemaccording to an embodiment of the present invention. In the basicenvironment, the RRMP scheduler transmits the RLP packet to the RMCP,and the RMCP buffers the RLP packets received from the BSC and sends anSCH assignment request to the RRMP. In FIG. 7, BTS-A refers to aselected BTS, and BTS-B refers to an old BTS.

[0115] Referring to FIG. 7, the MCCP of the BSC sends pilot strengthinformation of the corresponding mobile station (MS) to the MMCP in step701. In this connection, if a report interval (or transmission duration)of PSMM (Pilot Strength Measurement Message)/PSMMM (Pilot strengthMeasurement Mini Message) of the mobile station is equal to that of PMRM(Power Measurement Report Message), the reverse link quality will bedecreased. Accordingly, in this case, it is preferable for the mobilestation to asynchronize the transmission time with the frame level.

[0116] In steps 702 and 703, the RIMP of the BTS-A sends informationabout available power for the SCH to the RRMP and RMCP. Sending theavailable power information from the RIMP to the RRMP is to determinethe data rate of the SCH, and sending the available power informationfrom the RIMP to the RMCP is to select a leg. Then, in step 704, theRMCP sends the available power information received from the RIMP andthe last transmitted RLP sequence to the MMCP through the inband path.Here, the reason that the RMCP transmits the sequence number of the lasttransmitted RLP to the mobile station is to support the DTX function.That is, in the embodiment of the present invention, the BTS controlstransmission of the RLP frame according to the environment of thechannel link. Specifically, the BTS buffers the internal RLP frameinformation, and then controls transmission of the buffered RLP frameinformation according to the channel environment. Therefore, the BTSdoes not send an RLP retransmission request to the BSC, and instead,simply transmits the last number of the presently transmitted RLP frameto the BSC. Since the BSC knows the size of the RLP frame transmittedfrom the BTS, the BSC can determine the RLP frame transmission status ofthe BTS according to the RLP frame number reported from the BTS.

[0117] Upon receipt of the available power information and the lasttransmitted RLP sequence number from the RMCP, the MMCP sends the pilotstrength information of the corresponding mobile station, received instep 701, to the RMCP through the inband path, in step 705. Thereafter,in step 706, the RMCP sends the pilot strength information of the mobilestation received from the MMCP to the RRMP.

[0118] In steps 712 to 716, the BTS-B also transmits the available powerfor the SCH and the last transmitted RLP frame number to the BSC in thesame process as performed in the steps 702 to 706 by the BTS-A. Here,the BTS-A and the BTS-B become the legs for a specific mobile station.

[0119] If there are two legs for a specific mobile station as statedabove, the MMCP performs a leg selection algorithm in step 750. Adetailed description of the leg selection algorithm will be made laterwith reference to FIG. 8. If the leg is changed by the leg selectionalgorithm, the MMCP sends a handoff indication message to the RMCP-B (orold RMCP) through the inband path in step 717. Upon receipt of thehandoff indication message, the RMCP-B flushes the buffer aftertransmitting the RLP packet until the assigned data transmissionduration, if assignment of the SCH to the mobile station is notcompleted. The packet sequence last transmitted by the RMCP-B istransmitted to the MMCP in the same method as performed in step 704.

[0120] In step 758, the MMCP sends the RLP frame to the RMCP-A of theBTS which is to assign the SCH to the corresponding mobile station.Transmission of the RLP frame is performed by a flow control algorithmbetween the MMCP and the RMCP-A, and the transmission amount isdetermined such that a buffer capacity of the RMCP-A for the mobilestation should maintain a specific boundary. Then, in step 759, theRMCP-A periodically or separately sends SCH assignment request messagesincluding the RLP Q-Size information of the mobile stations to the RRMP.

[0121] In step 760, the RRMP-A performs SCH scheduling in the samemethod as described in FIG. 5. Thereafter, in step 770, the RRMP-A sendsSCH assignment information for the mobile station to the RMCP-Aaccording to the scheduling results determined by the scheduler. In step771, the RMCP-A then sends the SCH assignment information to the MMCPthrough the inband path according to the scheduling results determinedby the scheduler. In reply to the SCH assignment message, the MMCP sendsan SCH assignment command to the MCCP in step 772. The MCCP thenperforms a process for transmitting and receiving SCH assignmentmessages for the mobile station in step 773. In this case, aretransmission function of L2 (Layer-2) is not applied to the ESCAM.Upon receipt of the ESCAM transmitted from the MCCP, the mobile stationcan additionally send an acknowledgement signal ACK for the ESCAM instep 774.

[0122] Thereafter, in step 775, the RMCP-A transmits the RLP packet tothe mobile station at the start time for the data transmission duration,and in the DTX mode, the RMCP-A defers transmitting the RLP packet.Further, the RMCP-A transmits a sequence number of the last transmittedRLP frame to the MMCP through the inband path as in the step 704. Inaddition, RLP retransmission due to occurrence of an RLP frame error isperformed between the MMCP of the BSC and the RLP of the mobile stationat step 776.

[0123] In the leg selection process of step 750, if there are two ormore legs for the mobile station, the MMCP performs an operation ofselecting a leg for the mobile station by activating the leg selectionalgorithm. Further, the SCH scheduling process of step 760 is performedas described in FIG. 5, and in this process, the RRMP selects the mobilestation to be assigned the SCH according to the PFQ algorithm, based onthe RLP buffer size reported from the RMCP, and calculates a start pointof the assigned SCH and an end point of the data transmission durationof the radio traffic channel.

[0124] The embodiment of the present invention provides the legselection algorithm, taking into consideration the case where the mobilestation performs a handoff through the FCH and the DCCH. In this case,the mobile station is in the state where the mobile station communicateswith two BTSs (i.e., a handoff state where two BTSs are connected to onemobile station through the FCH and/or the DCCH). Therefore, two legs areconnected to the BSC for the old BTS and a new BTS. Since the SCH has afat pipe structure in which one or a small number of channels are used,the SCH consumes very high transmission power as compared with the FCHor the DCCH. Therefore, when the SCH is connected to two or more legs inthe handoff state, there occur large noises. Hence, it is preferablethat the SCH should be connected to one leg even in the handoff state.

[0125] First, as an information collecting time unit, a PMRM reportinterval is a minimum of 180 ms, and 260 ms, 280 ms, 340 ms, 360 ms, 420ms, 440 ms and 480 ms (5*2^(n)+4*k frames) are available for the PMRMreport interval. The PSMM and the PSMMM are not periodic. For theperiodic PSMM order, the minimum period is 800 ms. In addition, when thePSMM transmission duration of the mobile station is identical to thePMRM transmission duration, the reverse link quality is decreased.Hence, it is preferable to asynchronously transmit data between themobile stations with the frame level.

[0126] An operating position of the leg selection algorithm is definedby the MMCP.

[0127] With regard to an operating interval of the leg selectionalgorithm, leg selection frames for the respective users are notsynchronized with one another (Frame Asynchronous). In the embodiment ofthe present invention, the PMRM interval for the data call is set to 260ms. Further, the leg selection results are provided to the RRMP throughthe RMCP.

[0128] In this case, there are two types of information necessary forthe leg selection from the BTS, for the respective legs, as shown inFIG. 7. As for the first information, the respective BTSs transmit theinformation about the available power for the SCH to the BSC as shown inFIG. 7. Here, since there is no direct path from the RRMP to the MMCP,the BTS transmits the available power information to the BSC through anin-band path from the RMCP to the MMCP. The second information is thepilot strength information. For the pilot strength information, the MCCPuses the last value obtained by processing the PMRM, PSMM or PSMMM.

[0129]FIG. 8 shows an algorithm for selecting a leg in the BSC using theabove information.

[0130] Referring to FIG. 8, in step 811, a soft handoff is started for adedicated channel (FCH/DCCH in the CDMA system; hereinafter referred toas “FDCH”) for transmitting control information (FDCH Soft HandoffStart). In step 813, it is determined whether the FDCH soft handoff hasended. If the FDCH soft handoff has ended, the BSC selects thehanded-off FDCH leg in step 831.

[0131] Otherwise, if the FDCH soft handoff has not ended in step 813,the BSC receives the pilot strength information of PMRM, PSMM or PSMMMin step 815. Thereafter, the BSC finds a leg for maximizing a rateindicator in step 817. Here, the found leg can be either the presentlyconnected old leg or a new leg. After finding the leg, the BSCdetermines in step 819 whether the found leg is an old leg. If the foundleg is the old leg, it means that the present leg has a better conditionthan the new leg. Thus, the BSC selects the found leg as the old leg instep 821.

[0132] However, if the found leg is not the old leg in step 819, the BSCdetermines in step 825 whether a rate indicator of the new leg is largerthan the sum of a rate indicator of the old leg and a hysteresis value(LEG_Sel_Hysteresis) set for the leg selection. That is, in theembodiment of the present invention, the new leg is selected as the oldleg, when the rate indicator of the new leg is larger than the rateindicator of the old leg and the set hysteresis value is satisfied.Therefore, when the above condition is not satisfied in step 825, theBSC proceeds to step 821 to select the old leg. Otherwise, when thecondition is satisfied, the BSC selects the new leg in step 827.

[0133] After selecting the leg in step 821 or 827, the BSC determinesthe selected leg as the old leg in step 823 and returns to step 813. Bydoing so, the BSC selects the BTS having the higher data rate out of thetwo or more BTSs connected to the mobile station in the soft handoffstate.

[0134] The leg selection algorithm will be described more specifically.

[0135] When selecting a leg by activating the leg selection algorithm,the MMCP of the base station controller (BSC) receives pilot strengthfrom the MCCP and available power values for the SCH from the RIMP ofeach BTS. The MMCP first calculates a data rate serviceable in each legfor the mobile station, and then, selects the BTS supporting the highestdata rate out of the data rates calculated for the two or more legs.

[0136] A description of the invention will be made with reference to afirst embodiment in which available rates (Available SCH Power (LEG)) ofeach leg are first calculated and then the leg having the highest rate(Rate_achiev) is selected, and a second embodiment in which availablerate indicators (Rate_indicator) of each leg are first calculated andthen the leg having the highest rate indicator value is selected.

[0137] First, a description will be made of the first embodiment forselecting the leg having the highest Rate_achiev after calculating theavailable rates Rate_achiev of respective legs.

[0138] The available rates Rate_achiev in each leg for the user arecalculated as follows, on the assumption that the entire available SCHpower is used by the user. Here, it will be assumed that the pilot power(Pilot Power (LEG)) is known to the MMCP because the BSC uses one staticvalue for the pilot power.

[0139] The available rates Rate_achiev of the respective legs aredetermined as follows, using the available SCH power of the legs, thepilot power of the legs, pilot Ec/Io provided from the mobile station,and an Eb/Nt value necessary for maintaining the performance.

Rate_achiev (LEG)=f(Available SCH Power (LEG)/Pilot Power (LEG), Pilotrx Ec/Io (LEG), Req Eb/Nt table)

[0140] First, an SCH offset, which is a ratio of the available SCH powerto the pilot power, is calculated using the available SCH power and thepilot power.

SCH offset=(Available SCH Power)/(Pilot Power)

[0141] In this case, the maximum processing gain (pg), which can beassigned for the available SCH power, is calculated as follows.

pg=Req Eb/Nt/(Pilot Ec/Io*SCH_offset)

[0142] where Req Eb/Nt indicates a reception Eb/Nt value at the mobilestation, which is previously known through simulation, and Pilot Ec/Ioindicates a pilot reception Ec/Io value provide from the mobile stationthrough the signaling messages such as the PMRM or PSMM.

[0143] Finally, the available rate is determined as follows, since theprocessing gain at the rate of 9.6 Kbps is 128.

Rate_achiev=128/pg*9.6 kbps

[0144] When there are several legs, the BSC selects the BTS supportingthe highest rate out of the available rates Rate_achiev calculated forthe respective legs and performs data transmission on the selected leg.

[0145] The packet is not scheduled until the selected leg is scheduledin the RRMP, if a reverse SER (Symbol Error Ratio) is higher than a setthreshold SER_BAD_THRESH when the reverse FCH is assigned, or if thereverse pilot Ec/Nt is lower than a set threshold RPICH_BAD_THRESH whenthe reverse DCCH is assigned.

[0146] Next, a description will be made of the second embodiment forselecting the leg having the highest Rate_indicator after calculatingthe available rate indicators Rate_indicator of respective legs. In thisembodiment, the rate indictor Rate_indicator can be calculated by

Rate_indicator(leg)=Pilot Strength dB(leg)+Available_SCH_Power dB(leg)

[0147] A leg selection algorithm according to the second embodiment ofthe present invention is given as follows using the Rate_indicator.

[0148] In this case, the rate indicators of the respective legs arecalculated using the pilot Ec/Io provided from the mobile station andthe available SCH power, and then the leg having the highest rateindicator value is selected.

[0149] for (each leg in the Active Set)

Rate_indicator(leg)=Pilot_Strength_dB(leg)+Available_SCH_Power_dB (leg);

Leg=argmaxleg(Rate_indicator(leg);

[0150] That is, the leg having the high reception pilot power at themobile station and having the high available SCH power is selected forthe data service.

[0151] Meanwhile, in order to prevent a ping-pong phenomenon in thehandoff area, the data service is continuously performed in the existingleg when the rate indicator value of the newly determined leg is smallerthan the rate indicator value of the previous leg plus the hysteresisvalue. if (Leg == Old_Leg) { Selected_Leg= Old_Leg; } else if (New Leg!= Old_Leg) { if (Rate_indicator(Leg) > Rate_Indicator(Old_Leg) +Leg_Sel_Hysteresis) Selected_Leg=Leg; else Selected_Leg= Old_Leg; }Old_Leg=Selected_Leg

[0152] The leg selection method according to the second embodiment ofthe present invention is performed as shown in the process of FIG. 8,and the Rate_indicator is used for the Rate_achiev of the firstembodiment. Here, the Rate_indicator is the pilot strength (dB) plus theavailable SCH power (dB), and the base station controller (BSC) selectsthe BTS having the highest Rate_indicator value after calculating therate indicator values Rate_indicator of the base transceiver systems(BTSs) in the handoff state. In the leg selection process, a new leg isselected when the condition ofRate_indicator(Leg)>Rate_indicator(Old_Leg)+Leg_Sel_Hysteresis issatisfied.

[0153] In addition, the packet is not scheduled until the selected legis scheduled in the RRMP, if the reverse SER is higher than a setthreshold SER_BAD_THRESH when the reverse FCH is assigned, or if thereverse pilot Ec/Nt is lower than a set threshold RPICH_BAD_THRESH whenthe reverse DCCH is assigned.

[0154] The SCH scheduling and assignment method according to theembodiment of the present invention has the following advantages.

[0155] (1) By assigning the SCH according to the embodiment of thepresent invention, it is possible to efficiently support the limitedradio resources. (2) The embodiment of the present invention can assignthe radio channel to the mobile stations by the scheduling concept.Therefore, it is possible to maximize utilization efficiency of theradio channels by minimizing the duration where there exists no radiochannel resource. (3) The embodiment of the present invention can fairlyprovide service to a plurality of users through the scheduling concept.(4) The embodiment of the present invention can support the quality ofservice (QoS) desired by the system operator by applying the PFQ (PseudoFair Queuing) algorithm as requested by the system operator.

[0156] While the invention has been shown and described with referenceto a certain preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and detail may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A method for assigning packet data to betransmitted to a radio packet data channel of a base station system inresponse to packet traffic transmission requests for a plurality ofmobile stations in a mobile communication system, the method comprisingthe steps of: collecting the packet traffic transmission requests of theradio packet data channel for the mobile stations; selecting at leastone of the mobile stations from the collected packet traffictransmission requests; transmitting to each selected mobile station achannel assignment message including information about a data rate, adata transmission duration and a start time of the data transmissiondurations for the selected mobile station; and transmitting the packetdata to the selected mobile station at the start time of the datatransmission durations at the data rate.
 2. The method as claimed inclaim 1 , wherein the step of selecting the mobile station intended touse the radio packet data channel comprises the step of selectingcandidate mobile stations by a PFQ (Pseudo Fair Queuing) algorithm. 3.The method as claimed in claim 2 , wherein the step of selecting themobile station intended to use the radio packet data channel comprisesthe step of first selecting a mobile station which used the radio packetdata channel in a previous state, out of the candidate mobile stations.4. The method as claimed in claim 2 , wherein the step of selecting themobile station intended to use the radio packet data channel comprisesthe step of first selecting mobile stations having different frameoffsets, out of the candidate mobile stations.
 5. The method as claimedin claim 1 , wherein the step of transmitting the channel assignmentmessages to the mobile stations intended to use the radio packet datachannel comprises the step of dispersedly transmitting the channelassignment messages based on the start points of the data transmissiondurations.
 6. The method as claimed in claim 1 , wherein the radiopacket data channel is a supplemental channel (SCH).
 7. A method forscheduling and assigning a radio packet data channel in a base stationsystem for a mobile communication system, the method comprising thesteps of: collecting, in a first scheduling interval, the packet traffictransmission requests of the radio packet data channel, transmitted frommobile stations; selecting, in a second scheduling interval, at leastone mobile station intended to use the radio packet data channel byscheduling the packet traffic transmission requests, determining a datarate, a data transmission duration and a start time to be used by theselected mobile station, and generating a channel assignment message forthe radio packet data channel, the channel assignment message includinginformation about the determined data rate, data transmission durationand start time; and transmitting, in a third scheduling interval, packetdata for the corresponding mobile station at a start point of thecorresponding data transmission duration of the respective mobilestations to which the radio packet data channel is sequentiallyassigned, ending transmission of the radio packet data at an end pointof the last assigned data transmission duration of the mobile station,and transmitting the packet data to the last mobile station assigned. 8.The method as claimed in claim 7 , wherein the scheduling intervalincludes at least two data transmission durations.
 9. The method asclaimed in claim 8 , wherein the data transmission duration is N (N=1,2, 3, . . . ) times a frame size of the radio packet data channel. 10.The method as claimed in claim 9 , wherein the radio packet data channelincludes 20 ms frames.
 11. The method as claimed in claim 7 , whereinthe scheduling interval includes a guard interval for preventing frameoffset collision of the mobile station which is assigned at least twodata transmission durations and the radio packet data channel.
 12. Themethod as claimed in claim 7 , wherein the step of transmitting thechannel assignment messages to the mobile stations intended to use theradio packet data channel comprises the step of dispersedly transmittingthe channel assignment messages based on the start points of the datatransmission duration.
 13. An apparatus for assigning packet data to betransmitted to a radio packet data channel of a base station system inresponse to a packet traffic transmission request for a plurality ofmobile stations in a mobile communication system, the apparatuscomprising: a collector for collecting the packet traffic transmissionrequests of the radio packet data channel for the mobile stations; ascheduler for selecting at least one of the mobile stations from thecollected packet traffic transmission requests; a message generator forgenerating a channel assignment message including information about adata rate, a data transmission duration and a start time of the radiopacket data channel and start points of the data transmission durationsfor the selected mobile station, and transmitting the generated channelassignment message to the selected mobile station; and a transmissiondevice for transmitting the packet data to the selected mobile stationat the start points of the data transmission durations at the data rate.